Hydrophobic thin-film composite membranes for non-polar organic solvent nanofiltration

Abstract

Organic solvent nanofiltration (OSN) is a membrane-based technique that separate molecules ranging between 100–2000 g mol–1. OSN has emerged as a promising alternative for applications in the petrochemical industry. Most OSN membranes are either integrally skinned asymmetric (ISA) or thin-film composites (TFC). Interfacially polymerized TFC membranes have been identified as potential OSN membranes with separation at a molecular level. Recent research showed the limitation of interfacially polymerized and commercial membranes for non-polar solvent nanofiltration, which potentially deters membranes inadequate for solvent recovery and petroleum refineries application. This research aim to develop hydrophobic TFC membranes and understand their structure-function-performance relationships. Novel high-flux hydrophobic TFC membranes were developed, elucidated, and studied. The surface properties of hydrophilic TFC OSN membranes were modified by incorporating different monomers containing hydrophobic groups. Surface polarity and membrane performance have been studied in detail, suggesting that surface chemistry plays an important role in solvent permeation.

Firstly, a novel hydrophobic TFC membrane was developed to enhance the performance of non-polar solvents. I proposed a new fluorinated monomer, 4,4ʹ-(hexafluoroisopropylidene) bis (benzoyl chloride) (HFBC), as co-monomer for the organic phases. The polyamide (PA) nanofilm was prepared by interfacially reacting trimesoyl chloride (TMC) and 4,4ʹ-(hexafluoroisopropylidene)bis(benzoyl chloride) (HFBC) in an organic phase with 5-trifluoromethyl-1,3-phenylenediamine (TFMPD) in an aqueous phase in a single step. The new surface modification strategy led to improve the interaction between the non-polar solvents and membrane surface. This research revealed the ability to increase in non-polar solvents permeance, including toluene and hexane. Secondly, I proposed a simple and rapid method for fabricating fluorinated covalent organic polymer (COP) membranes for OSN. To create a fluorine-rich polymer backbone, I used the fluorinated monomer as an organic phase monomer for the interfacial polymerization (IP) process. The resulting TFC membranes exhibited hydrophobic surface properties and showed good chemical stability. The fabricated hydrophobic TFC membranes have excellent permeances for non-polar solvents such as toluene, heptane, and hexane. Thirdly, highly performance TFC membranes have been developed via IP by controlling the structure of the top layer. This was achieved by incorporating a monomer with a contorted structure during the IP reaction using 4, 4’-(perfluoropropane-2, 2-diyl) diphthaloyl dichloride (6FTAC) as an organic co-monomer and TMC. The fabricated hydrophobic TFC membranes could transport hydrocarbon liquids and demonstrated promising results in fractionating crude oil.